The use of coagulants or flocculants to clarify aqueous systems is well known in the art. For example, these agents can be used to remove solids such as color bodies from pulp/papermill and municipal wastewater systems. However, the ability to simply, inexpensively and automatically control the feed of coagulants or flocculants to such systems based on an on-line indication of the effluent quality of the system being treated is not believed to be presently available. Such a capability would constitute a notable advance of the art. For example, it would be desirable to regulate the dosage of a coagulant or flocculant so as to achieve an effluent color or turbidity specification, while minimizing the costs associated with coagulant/flocculant application. The instant invention, which relies upon a tube clarifier to monitor and/or control clarification efficacy, accomplishes this objective.
Generally speaking, the instant invention relates to the separation or removal of solids such as suspended matter and/or color bodies from aqueous systems. As used herein, the term "separation process" is used to describe such processes. A preferred separation process, relative to use of the instant method, is a clarification process.
The prior art relies on the following methods to monitor clarification processes:
(a) Laboratory evaluation, which requires the taking of a sample, followed by measurement of effluent quality.
(b) Small scale simulation of the process, wherein a coagulant-treated stream is split and the side stream is passed through a small scale liquid-solid separation process, such as a small solids contact clarifier, filter, or settling chamber. The quality of the separated effluent is then measured. An example of such a device, where a small filter is used prior to turbidity measurement, is disclosed in "Water Treatment and Plant Design for the Practicing Engineer," Ann Arbor Science publishers, Inc. (1978) pp.300-302.
(c) Charge measurement by streaming current, wherein a side stream of a treated stream is passed through a streaming current measurement device. Charge neutralization is an indication of the expected effluent quality.
The streaming current principle is oftentimes used in applications where the suspended solids are low, where the water is clean (i.e., does not contain substantial amounts of oil or other municipal or industrial waste), and where the coagulant and flocculant dosages are low. However, the inventor is not aware of applications or publications which describe a successful use of stream current measurement in more severe applications.
(d) Flocculation analyzers which quantify the extent of flocculation by measuring changes in the number of solids particles present (e.g., particle counts) during a separation process.
These monitoring methods have several disadvantages. For example, the manual methods conducted in a laboratory cannot be run on a continuous basis. Small scale simulation techniques are expensive, and the complexity and reliability of related equipment generally precludes unattended operation.
While streaming current measurement has been found to be applicable in certain feed water clarification applications, such as in the clarification of drinking water and utility water for industrial plants, it has not been found to be applicable in the treatment of streams that contain high amounts of solids, waste treatment, or treatments requiring a high dosage of coagulant or flocculant. Finally, flocculation analyzers require sophisticated instrumentation. They function by incrementally increasing coagulant dosages in the sampled stream with concurrent observation of the resulting changes in effluent quality. The proper dosage is then inferred from the response, which is time-consuming and costly. These disadvantages are overcome by the instant invention.
Known references relating to the flocculation analyzers include:
UK 2,129,549 (May 1984) John Gregory & David William Nelson of University College London, "Detecting Particles And Changes In Particle Size In A Suspension"; and
U.S. Pat No. 4,752,131 (June 1988) J. Eisenlauer, D. Horn, W. Ditter & H. Eipel, "Laser System For Particle Dispersion Measurement Has Optical Fibres For Transmission From Laser And To Detector With Sample Flow Surrounded By Envelope Flow".
Also, commercially available flocculation analyzers include the Photometric Dispersion Analyzer PDA 2000, Rank Brothers Ltd., Cambridge, England, and the Flocculation Analyzer System 6000 from Pen Kem, Inc. Bedford Hills, N.Y. Settling devices known in the art include settling tubes, Lamellae sedimentation devices, and inclined plate clarifiers. However, the instant use of tube clarifiers is completely novel.
For a discussion of settling tubes, see "Water Treatment and Plant Design for the Practicing Engineer," Ann Arbor Science Publishers, Inc. (1978) pp. 178-179, 302-307. These devices enhance the separation of clarified effluent from sedimenting solids. However, a key distinction between these devices and the instant tube clarifier is that the instant tube clarifier allows coagulation and/or flocculation to go to completion without physical separation of the effluent from the solids. Also, in the instant method, slugs of solids are carried by the carrier liquid.